Synthesis method for polymers by controlled radical polymerisation with xanthates

ABSTRACT

A polymer composition and method of preparing same is described wherein an ethylenically unsaturated monomer is contacted with a source of free radicals and a compound of formula (1A), (1B) and (1C) as defined herein. The polymer composition may be a homopolymer or a block copolymer.

The present invention relates to a novel method for “controlled” or“live” radical polymerisation leading to polymers, especially blockcopolymers.

Block polymers are normally prepared by ionic polymerisation. That typeof polymerisation has the disadvantage of permitting the polymerisationof only specific types of non-polar monomer, especially styrene andbutadiene, and of requiring a particularly pure reaction medium andtemperatures often lower than the ambient temperature in order tominimise parasitic reactions, thus giving rise to major implementationconstraints.

Radical polymerisation has the advantage of being easy to implementwithout respecting excessive conditions of purity and at temperaturesequal to or higher than the ambient temperature. However, untilrecently, there was no radical polymerisation method enabling blockpolymers to be obtained.

Since then, a novel radical polymerisation method has been developed:the method involved is so-called “controlled” or “live” radicalpolymerisation. Radical polymerisation proceeds by growth by propagationof macro-radicals. Those macro-radicals, which have a very short life,recombine irreversibly by coupling or dismutation. When polymerisationtakes place in the presence of several comonomers, the variation in thecomposition of the mixture is extremely slight considering the life ofthe macro-radical, so that the chains have a random chain formation fromthe monomer units and not a block chain formation.

Recently, techniques for controlled radical polymerisation have beendeveloped in which the ends of polymer chains can be reactivated intothe form of a radical by homolytic bond cleavage (for example C—O, orC-Halogen).

Controlled radical polymerisation therefore has the followingdistinctive aspects:

-   -   1. The number of chains is fixed throughout the duration of the        reaction,    -   2. The chains all grow at the same rate, which translates into:        -   a linear increase in the molar masses with the conversion,        -   a narrow mass distribution,    -   3. The average molar mass is controlled by the molar ratio of        the monomer to the chain precursor,    -   4. The possibility of preparing block copolymers.

The controlled character is all the more marked because the rate ofreactivation of the chains into radical form is very high consideringthe rate of growth of the chains (propagation). There are cases in whichthis is not always true (i.e. the rate of reactivation of the chainsinto: radical form is higher than or equal to the rate of propagation)and conditions 1 and 2 are not observed. Nevertheless, it is stillpossible to prepare block copolymers.

WO 98/58974 describes a live radical polymerisation method enablingblock copolymers to be obtained by a method without UV irradiation, byusing xanthate compounds, the properties of which are:

That radical polymerisation enables block polymers to be prepared in theabsence of a UV source, using any type of monomer. The polymers obtaineddo not contain metallic impurities which would militate against theiruse. They are functionalised at the end of the chain and have a lowindex of polydispersion of less than 2 and even less than 1.5.

One object of the present invention is to propose a novel polymerisationmethod using novel precursors of the xanthate type.

Another object is to propose a polymerisation method using precursors ofthe xanthate type, in the course of which the number-average molarmasses M_(n) of the polymers obtained are well controlled, that is tosay, close to the theoretical values M_(n th), this being throughout thepolymerisation reaction.

Another object is to propose a polymerisation method using precursors ofthe xanthate type for the synthesis of block copolymers and homopolymershaving a polydispersion index (M_(w)/M_(n)) which is low, that is tosay, close to 1.

The work of the inventors has resulted in a method for radicalpolymerisation in which block copolymers or homopolymers can be preparedin accordance with a process having remarkable and substantially greatercontrol than the methods known hitherto.

This method uses xanthates of a particular type which themselvesconstitute novel molecules.

The invention therefore relates to a method for the preparation ofpolymers, characterised in that there are brought into contact with oneanother:

-   -   at least one ethylenically unsaturated monomer,    -   at least one source of free radicals, and    -   at least one compound (I) of the general formula (IA), (IB) or        (IC):        in which:    -   R² and R^(2′), which may be identical or different, represent a        group of the formula:        in which:    -   R³ and R⁴, which may be identical or different, are selected        from a halogen group, —NO₂, —SO₃R, —NCO, CN, R, —OR, —SR, —NR₂,        —COOR, O₂CR, —CONR₂, —NCOR₂, C_(n)F_(2n+1) with n being 1 to 20,        preferably 1,        -   in which the groups R, which may be identical or different,            represent H or a group selected from:        -   alkyl,        -   alkenyl,        -   alkynyl,        -   cycloalkenyl,        -   cycloalkynyl,        -   aryl, optionally fused to an aromatic or non-aromatic            heterocycle,        -   alkaryl,        -   aralkyl,        -   heteroaryl,        -   which are optionally substituted by one or more identical or            different groups selected from halogen, ═O, ═S, OH, alkoxy,            SH, thioalkoxy, NH₂, mono- or di-alkylamino, CN, COOH,            ester, amide, C_(n)F_(2n+1) (n being 1 to 20), and/or            optionally interrupted by one or more atoms selected from O,            S, N, P,        -   or a heterocyclic group optionally substituted by one or            more groups such as defined above,    -   or R³ and R⁴, together with the carbon atom to which they are        attached, form a group ═O or ═S or a hydrocarbon ring or a        heterocycle,    -   R⁵ and R⁶, which may be identical or different, represent a        group such as defined above for R,    -   or R⁵ and R⁶ together form a C₂-C₄ hydrocarbon chain optionally        interrupted by a hetero atom selected from O, S, N and P,        -   R¹ and R^(1′), which may be identical or different,            represent a group such as defined above for R³ or R⁴,        -   p represents an integer from 2 to 10.

According to the invention, the term “alkyl” denotes a linear orbranched hydrocarbon radical containing from 1 to 20 carbon atoms, suchas methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl,pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl oricosyl.

“Alkenyl” means a linear or branched hydrocarbon chain of from 2 to 20carbon atoms comprising one or more double bonds. Examples ofparticularly preferred alkenyl groups are alkenyl groups carrying asingle double bond, such as —CH₂—CH₂—CH═C(CH₃)₂, vinyl or allyl.

“Alkynyl” means a linear or branched hydrocarbon chain of from 2 to 20carbon atoms comprising one or more triple bonds. Examples ofparticularly preferred alkynyl groups are alkynyl groups carrying asingle triple bond, such as —CH₂—CH₂—C═CH.

The term “cycloalkyl” denotes saturated hydrocarbon groups which may bemonocyclic or polycyclic and which comprise from 3 to 12 carbon atoms,preferably from 3 to 8 carbon atoms. Monocyclic cycloalkyl groups, suchas cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl aremore particularly preferred.

According to the invention, “cycloalkenyl” means a group derived from acycloalkyl group as defined above, having one or more double bonds,preferably one double bond.

According to the invention, “cycloalkynyl” means a group derived from acycloalkyl group as defined above, having one or more triple bonds,preferably one triple bond.

The term “aryl” represents an aromatic monocyclic or bicyclichydrocarbon group comprising from 6 to 10 carbon atoms, such as phenylor naphthyl.

“Alkaryl” means an aryl group as defined above, substituted by an alkylgroup.

“Aralkyl” means an alkyl group as defined above, substituted by an arylgroup.

“Alkoxy” means an O-alkyl group generally having from 1 to 26 carbonatoms, especially methoxy, ethoxy, propoxy and butoxy.

“Halogen” means a fluorine, chlorine, bromine or iodine atom.

When the alkyl group is optionally halogenated, it preferably representsperfluoroalkyl and especially pentafluoroethyl or trifluoromethyl.

The term “heteroaryl” denotes aromatic groups which are monocyclic withfrom 5 to 7 chain members or bicyclic with from 6 to 12 chain membersand which comprise one, two or three endocyclic hetero atoms selectedfrom O, N and S. Examples thereof are the groups furyl, thienyl,pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl,pyrazolyl, oxadiazolyl, triazolyl, thiadiazolyl, pyridyl, pyridazinyl,pyrazinyl and triazinyl.

Preferred heteroaryls comprise 4 or 5 carbon atoms and 1 or 2 heteroatoms.

The term heterocyclic group denotes monocyclic or bicyclic saturated orpreferably unsaturated carbon rings having from 5 to 12 chain membersand 1, 2 or 3 endocyclic hetero atoms selected from O, N and S. Theseare generally derivatives of the heteroaryl groups described above.

Preferably, when it is unsaturated, the heterocycle comprises a singledouble bond. Preferred examples of unsaturated heterocycles aredihydrofuryl, dihydrothienyl, dihydropyrrolyl, pyrrolinyl, oxazolinyl,thiazolinyl, imidazolinyl, pyrazolinyl, isoxazolinyl, isothiazolinyl,oxadiazolinyl, pyranyl and the mono-unsaturated derivatives ofpiperidine, of dioxane, of piperazine, of trithiane, of morpholine, ofdithiane, of thiomorpholine, and also tetrahydropyridazinyl,tetrahydropyrimidinyl and tetrahydrotriazinyl.

When one of the above groups represents an aryl group optionally fusedto an unsaturated heterocycle, the unsaturated heterocycle has from 5 to7 chain members and preferably a single unsaturation in common with thearyl group.

The method according to the invention therefore consists in bringinginto contact with one another a source of free radicals, anethylenically unsaturated monomer and a compound (I) of formula (IA),IB) or (IC).

The compound (I) carries a xanthate function. According to the essentialfeature of the invention, the xanthate function carries a group R² orR^(2′) which is substituted by a group P(O)(OR⁵)(OR⁶) such as definedabove.

Advantageously, the group R³ is an electron-attracting group.

According to a preferred variant, R² represents a group such as definedabove and R³ represents an alkyl group substituted by at least onefluorine, chlorine and/or bromine atom. The preferred groups R³ are thefollowing:

-   -   CF₃    -   CF₂CF₂CF₃    -   C₆F₁₆,

According to another preferred variant, R³ represents a group CN or NO₂.

Advantageously, R⁴ represents a hydrogen atom. The groups R⁵ and R⁶preferably represent a linear, branched or cyclic alkyl groupadvantageously containing from 1 to 20 carbon atoms.

There may be mentioned, in particular, the groups methyl, ethyl,isopropyl, propyl, butyl, isobutyl, tert-butyl, pentyl, n-pentyl, hexyl,cyclohexyl, heptyl, ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, hexadecyl, octadecyl.

Those groups may be present in the various possible isomeric forms.

R⁵ and R⁶ may also represent a substituted alkyl group comprising one ormore identical or different substituents. There may be mentioned, inparticular, the substituting groups acyl, such as acetyl; alkoxy, suchas methoxy, butoxy, phenyloxy, cyclohexyloxy; halo, especially chloroand fluoro; hydroxy; aryl, such as phenyl and naphthalenyl; aralkyl;alkenyl, especially hexenyl, cyclohexenyl and propenyl.

A particularly advantageous sub-group is constituted by alkyl groupssubstituted by one or more halogen atoms, preferably fluorine atoms, thegroup C_(n)F_((2n+1))—CH₂ (n being as defined above) being particularlypreferred.

R⁵ and R⁶ may also together form a cyclic group comprising a phosphorusatom, for example a group

The most valuable results were obtained for the compound (I) when R¹ isa group selected from:

-   -   CH(CH₃)(CO₂Et)    -   CH(CH₃)(C₆H₅)    -   CH(CO₂Et)₂    -   C(CH₃)(CO₂Et)(S—C₆H₅)    -   C(CH₃)₂(C₆H₅), et        in which Et represents an ethyl group and Ph represents a phenyl        group.

The groups R¹ and R^(1′) may also represent a polymer chain resultingfrom radical or ionic polymerisation or resulting from polycondensation.Preferred compounds of formula (IC) are those in which R^(1′) is thegroup —CH₂-phenyl-CH₂— or the group —CHCH₃CO₂CH₂CH₂CO₂CHCH₃—.

R² is preferably a group:

in which R³ is CF₃, CF₂CF₂CF₃, C₆F₁₃ or CN and R⁵ is a C₁-C₄ alkylgroup, preferably ethyl.

According to the preferred form of the invention, the polymerisationmethod uses a compound (I) of formula (IA). The preferred compounds offormula (IA) are the following:

The compounds of formula (IA) may, in particular, be obtained by:

-   -   a) reacting a carbonyl compound of the general formula II:        R³ and R⁴ being as defined above, with a phosphite of the        general formula III:        R⁵ and R⁶ being as defined above,    -   to form a compound of the general formula IV:        R³, R⁴, R⁵ and R⁶ being as defined above,    -   b) reacting the compound of formula IV with carbon disulphide        CS₂ in the presence of a metal alcoholate M⁺OR′⁻ to yield a        xanthate of formula V:        R²O (C═S)—S⁻, M⁺  (V)        in which R² is as defined above and M represents a cation,        especially an alkali metal cation;    -   c) reacting the compound of formula V with a compound of formula        VI:        R¹X   (VI)        in which R¹ is as defined above and X-represents a halogen atom,        to yield the compound of formula (IA) as defined above.

The compounds of the general formula IB are obtained in the same mannerstarting from polyhydroxylated compounds corresponding to the alcohol ofthe general formula IV.

The compounds of the general formula IC are obtained in the same mannerstarting from the polyhalogenated analogue of the alkyl halide of thegeneral formula VI.

The compounds of the general formula II are commercially available orcan be readily prepared by the person skilled in the art usingconventional procedures.

The phosphites of the general formula III can thus be prepared byreaction between an alcohol and PCl₃ in a manner known to the personskilled in the art. When the groups R⁵ and/or R⁶ have a high carbonnumber, it is preferable first of all to prepare phosphites having a lowmolecular weight, for example a diethyl phosphite, and then, by atransesterification route, to replace the ethoxy groups by alkoxy groupshaving a higher molecular weight.

In the case of aromatic phosphites, it is preferred first of all toprepare triphenyl phosphite and to react it with phosphorous acid toobtain diphenyl phosphite.

The following phosphites may also be prepared:

-   -   dimethyl phosphite    -   diethyl phosphite    -   dipropyl phosphite    -   dibutyl phosphite    -   dipentyl phosphite    -   dihexyl phosphite    -   diheptyl phosphite    -   dioctyl phosphite    -   dinonyl phosphite    -   didecyl phosphite    -   diundecyl phosphite    -   didodecyl phosphite    -   ditridecyl phosphite    -   ditetradecyl phosphite    -   dihexadecyl phosphite    -   dioctadecyl phosphite    -   bis[2-(acetyloxy)ethyl]phosphite    -   bis(4-butoxybutyl)phosphite    -   bis[2-(cyclohexyloxy)methylethyl]phosphite    -   bis(methoxymethyl)phosphite    -   bis[2-chloro-1-(chloromethyl)ethyl]phosphite    -   bis(2-chloroethyl)phosphite    -   bis(2-chloropropyl)phosphite    -   bis(2,3-dihydroxypropyl)phosphite    -   bis(2-hydroxyethyl)phosphite    -   bis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl)phosphite    -   bis(2-fluoroethyl)phosphite    -   bis(2,2,3,3,4,4,5,5-octafluoropentyl)phosphite    -   bis(2,2,3,3-tetrafluoropropyl)phosphite    -   bis(2,2,2-trifluoroethyl)phosphite    -   2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptylmethyl phosphite    -   methyl 2,2,3,3,4,4,5,5-octafluoropentyl phosphite    -   methyl 2,2,3,3-tetrafluoropropyl phosphite    -   diphenyl phosphite    -   bis(4-methylphenyl)phosphite    -   bis(4-nonylphenyl)phosphite    -   di-1-naphthalenyl phosphite    -   dicyclohexyl phosphite    -   di-2-cyclohexen-1-yl phosphite    -   di-2-propenyl phosphite    -   2,7-dioxo(2,7-H)-1,3,6,8-tetraoxa-2,7-diphosphocyclodecane

In the same manner as indicated above, it is possible to preparephosphites in which R⁵ and R⁶ are different, starting from thecorresponding compounds of different alcohols.

According to the method of the invention, the source of free radicals isgenerally a radical polymerisation initiator. However, in the case ofsome monomers, such as styrene, thermal initiation is sufficient togenerate free radicals.

In the first case, the radical polymerisation initiator may be selectedfrom the initiators conventionally used in radical polymerisation. Itmay be, for example, one of the following initiators:

-   -   hydrogen peroxides, such as: t-butyl hydroperoxide, cumene        hydroperoxide, t-butyl peroxyacetate, t-butyl peroxybenzoate,        t-butyl peroxyoctoate, t-butyl peroxyneodecanoate, t-butyl        peroxyisobutyrate, lauroyl peroxide, t-amyl peroxypivalate,        t-butyl peroxypivalate, dicumyl peroxide, benzoyl peroxide,        potassium persulphate, ammonium persulphate,    -   azo compounds, such as: 2,2′-azo-bis(isobutyronitrile),        2,2′-azo-bis(2-butyronitrile), 4,4′-azo-bis(4-pentanoic acid),        1,1′-azo-bis(cyclohexanecarbonitrile),        2-(t-butylazo)-2-cyanopropane,        2,2′-azo-bis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide,        2,2′-azo-bis(2-methyl-N-hydroxyethyl]propionamide,        2,2′-azo-bis(N,N′-dimethyleneisobutyramidine) dichloride,        2,2′-azo-bis(2-amidinopropane)dichloride,        2,2′-azo-bis(N,N′-dimethyleneisobutyramide),        2,2′-azo-bis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide),        2,2′-azo-bis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide),        2,2′-azo-bis[2-methyl-N-(2-hydroxyethyl)propionamide],        2,2′-azo-bis(isobutyramide)dihydrate,    -   redox systems comprising combinations such as:    -   mixtures of hydrogen peroxide, alkyl peroxide, peresters,        percarbonates and the like and of any one of the salts of iron,        titanium salts, zinc formaldehydesulphoxylate or sodium        formaldehydesulphoxylate, and reducing sugars,    -   the persulphates, perborate or perchlorate of alkali metals or        of ammonium in association with an alkali metal bisulphite, such        as sodium metabisulphite, and reducing sugars,    -   alkali metal persulphates in association with an arylphosphinic        acid, such as benzenephosphonic acid and the like, and reducing        sugars.

The quantity of initiator to be used is generally determined in such amanner that the quantity of radicals generated is a maximum of 20 mol. %relative to the quantity of compound (II), preferably a maximum of 5mol. %.

According to the method of the invention, the ethylenically unsaturatedmonomers are more especially selected from styrene and its derivatives,butadiene, chloroprene, (meth)acrylic esters, vinyl esters and vinylnitrites.

(Meth)acrylic esters means esters of acrylic acid and methacrylic acid,respectively, with hydrogenated or fluorinated C₁-C₁₂, preferably C₁-C₈,alcohols. Of the alcohols of that type there may be mentioned: methylacrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutylacrylate, 2-ethylhexyl acrylate, t-butyl acrylate, methyl methacrylate,ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate.

Vinyl nitrites include, more especially, those having from 3 to 12carbon atoms, such as, in particular, acrylonitrile andmethacrylonitrile.

It should be noted that styrene may be replaced completely or partiallyby derivatives, such as alphamethylstyrene or vinyltoluene.

Other ethylenically unsaturated monomers, which may be used alone or inadmixture, or which are copolymerisable with the above monomers areespecially:

-   -   carboxylic acid vinyl esters, such as vinyl acetate, vinyl        Versatate®, vinyl propionate,    -   vinyl halides,    -   ethylenically unsaturated mono- and di-carboxylic acids, such as        acrylic acid, methacrylic acid, itaconic acid, maleic acid,        fumaric acid and the mono-alkyl esters of dicarboxylic acids of        the type mentioned with alkanols preferably having from 1 to 4        carbon atoms and their N-substituted derivatives,    -   amides of unsaturated carboxylic acids, such as acrylamide,        methacrylamide, N-methylolacrylamide or        N-methylolmethacrylamide, N-alkylacrylamides,    -   ethylenically unsaturated monomers comprising a sulphonic acid        group and its alkali or ammonium salts, for example        vinylsulphonic acid, vinylbenzenesulphonic acid,        alpha-acrylamidomethylpropanesulphonic acid, 2-sulphoethylene        methacrylate,    -   vinylamine amides, especially vinylformamide or vinylacetamide,    -   ethylenically unsaturated monomers comprising a secondary,        tertiary or quaternary amino group, or a heterocyclic group        containing nitrogen, such as, for example, vinylpyridines,        vinylimidazole, aminoalkyl (meth)acrylates and aminoalkyl        (meth)acrylamides, such as dimethylaminoethyl acrylate or        methacrylate, di-tert-butylaminoethyl acrylate or methacrylate,        dimethylaminomethylacrylamide or        dimethylaminomethylmethacrylamide. It is also possible to use        zwitterionic monomers, such as, for example,        sulphopropyl(dimethyl)aminopropyl acrylate.

For the preparation of polyvinylamines, it is preferable to usevinylamine amides, for example vinylformamide or vinylacetamide, asethylenically unsaturated monomers. The polymer obtained is thenhydrolysed at an acid or basic pH.

For the preparation of polyvinyl alcohols, it is preferable to usecarboxylic acid vinyl esters, such as, for example, vinyl acetate, asethylenically unsaturated monomers. The polymer obtained is thenhydrolysed at an acid or basic pH.

The types and amounts of polymerisable monomers used according to thepresent invention vary in accordance with the particular finalapplication for which the polymer is intended. Those variations are wellknown and can be readily determined by the person skilled in the art.

The polymerisation can be carried out in bulk, in solution or inemulsion. It is preferably implemented in emulsion.

Preferably, the method is implemented in a semi-continuous manner.

The temperature may vary from ambient temperature to 150° C. dependingon the nature of the monomers used.

In general, in the course of polymerisation, the instantaneous contentof polymer relative to the instantaneous amount of monomer and polymeris from 50 to 99% by weight, preferably from 75 to 99%, and even morepreferably from 90 to 99%. That content is maintained in known manner bycontrolling the temperature and the rate of addition of the reagents andoptionally the polymerisation initiator.

Generally, the method is implemented in the absence of a UV source.

The method according to the invention has the advantage of permittingthe control of the number-average molar masses M_(n) of the polymers.Thus, those masses M_(n) are close to the theoretical values M_(n th),M_(n th) being expressed by the following formula:$M_{n\quad{th}} = {\frac{\lbrack M\rbrack_{0}}{\lbrack P\rbrack_{0}}\quad\frac{X}{100}M_{0}}$in which:

-   -   [M]₀ represents the initial molar concentration of monomer;    -   [P]₀ represents the initial concentration of precursor compound;    -   X represents the conversion of the monomer expressed as a        percentage;    -   M₀ represents the molar mass of the monomer (g/mol).

According to the present invention, the control of Mn is visible at thebeginning of polymerisation and remains present during the progress ofthe reaction.

In addition, the polymerisation method according to the presentinvention leads to polymers having a low index of polydispersion(lp=M_(w)/M_(n) with M_(w): weight-average molar mass) close to 1.

The invention therefore relates also to compositions which can beobtained by the method described above which consists in bringing intocontact with one another at least one ethylenically unsaturated monomer,at least one source of free radicals and at least one compound offormula (IA), (IB) or (IC).

Generally, those polymer compositions have a polydispersion index of atmost 2, preferably at most 1.5.

The invention relates also to a composition comprising predominantly apolymer of the general formula (IIIa):

in which:

-   -   R¹ and R² are as defined above;    -   V, V′, W and W′, which may be identical or different, represent        H, an alkyl group or halogen;    -   X, X′ Y and Y′, which may be identical or different, represent        H, a halogen or a group R⁷, OR⁷, O₂COR⁷, NHCOH, OH, NH₂, NHR⁷,        NR₂, R₂N⁺O⁻, NHCOR⁷, CO₂H, CO₂R⁷, CN, CONH₂, CONHR⁷ or CONR₂, in        which R⁷ is as defined above for R,    -   a and b, which may be identical or different, are 0or 1;    -   m and n, which may be identical or different, are higher than or        equal to 1, and when one or the other is higher than 1, the        repeating units are identical or different.

The invention relates more especially to a composition comprising ahomopolymer of the general formula (IIIA) as defined above in which therepeating units are identical, or a block copolymer of the generalformula (IIIA) as defined above in which the repeating units aredifferent.

The block polymers result from bringing into contact with one another:

-   -   an ethylenically unsaturated monomer of the formula:        CYY′(═CW—CW′)_(b)═CH₂,    -   a precursor polymer of the general formula (IIA):    -   and a source of free radicals.

The invention relates in particular to block polymers which have atleast two polymer blocks selected from the following associations:

-   -   polystyrene/poly(methyl acrylate),    -   polystyrene/poly(ethyl acrylate),    -   polystyrene/poly(tert-butyl acrylate),    -   poly(ethyl acrylate)/poly(vinyl acetate),    -   poly(butyl acrylate)/poly(vinyl acetate),    -   poly(tert-butyl acrylate)/poly(vinyl,acetate).

The invention relates also to a method for the preparation ofmulti-block block polymers in which the implementation of thepolymerization method described above is repeated at least once, using:

-   -   monomers differing from those used in the previous        implementation, and    -   instead of the compound (I) of formula (IA), (IB) or (IC), the        polymer resulting from the previous implementation, which is        called the precursor polymer.

The complete method for the synthesis of a block polymer according tothe invention may therefore consist in:

-   -   (1) synthesising a precursor polymer by bringing into contact        with one another an ethylenically unsaturated monomer, a source        of free radicals and a compound of formula (IA), (IB) or (IC),    -   (2) using the precursor polymer obtained in step (1) to prepare        a di-block block polymer by bringing that precursor polymer into        contact with a fresh ethylenically unsaturated monomer and a        source of free radicals.

Step (2) may be repeated as many times as desired with fresh monomers inorder to synthesise new blocks and thus to obtain a multi-block blockpolymer.

If the implementation is repeated once more, a tri-block block polymeris obtained and if it is repeated a second time, a “quadriblock” blockpolymer is obtained, and so on. Thus, at each fresh implementation, theproduct obtained is a block polymer having an additional polymer block.

For the preparation of multi-block block polymers, the method consistsin repeating the implementation of the previous method several times onthe block polymer resulting from each previous implementation withdifferent monomers.

The compounds of formula (IB) and (IC) are particularly valuable becausethey enable a polymer chain to be grown on at least two active sites.With that type of compound, it is possible to cut out polymerisationsteps to obtain a copolymer having n blocks. Thus, if p equals 2 informula (IB) or (IC), the first block is obtained by polymerising amonomer M1 in the presence of the compound of formula (IB) or (IC). Thatfirst block can then grow at each of its ends by polymerisation with asecond monomer M2 to form a tri-block copolymer. The tri-block polymercan itself grow at each of its ends by polymerisation with a thirdmonomer M3 to form a “pentablock” copolymer in only three steps. If p ishigher than 2, the method enables block copolymers or homopolymers to beobtained, the structure of which is “multi-armed” or hyper-branched.

According to this method for the preparation of multi-block polymers,when it is desired to obtain block polymers that are homogeneous andthat do not have a composition gradient, and if all of the successivepolymerisations are carried out in the same reactor, it is vital thatall of the monomers used in a step have been consumed before thepolymerisation of the following step commences and, therefore, beforethe fresh monomers are introduced.

As in the case of the method for the polymerisation of monoblockpolymers, this method for the polymerisation of block polymers has theadvantage of leading to block polymers having a low polydispersionindex. It also enables the molar mass of the block polymers to becontrolled.

The following Examples illustrate the invention without, however,limiting the scope thereof.

EXAMPLE 1 Preparation of2-[1-diethoxyphosphoryl)-2,2,2-trifluoroethoxythiocarbonylsulphanyl)-propionicacid ethyl ester (xanthate IAa)

Synthesis of 2,2,2-trifluoro-1-hydroxyethylphosphonic acid diethyl ester(alcohol IVa)

A solution of fluoral hydrate (10 g, 75% aqueous solution, 64.6 mmol)and of diethyl phosphite HP(O)(OEt)₂ (64.6 mmol) in triethylamine (9 ml,64.6 mmol) is agitated at ambient temperature for 15 hours. After rapidevaporation under reduced pressure (bath temperature lower than or equalto 40° C.), the liquid residue is purified by flash chromatography(petrol/acetone 10:1 then pure ether and ether/methanol 10:1) to givethe desired compound IVa with a yield of 82%.

IR (film) 3400, 2992, 2918, 1640, 1268 cm⁻¹; MS (IC) m/z 237 [MH]⁺; ¹HNMR (200 MHz, CDCl₃) δ 6.08 (sl, 1H), 4.12-4.38 (m, 5H), 1.33 (t, J=7.1Hz, 3H).

Synthesis of2-[1-diethoxyphosphoryl)-2,2,2-trifluoro-ethoxythiocarbonylsulphanyl)-propionicacid ethyl ester (xanthate IAa)

A solution of 5 g (21.18 mmol) of alcohol IVa in DMF (6 ml) is addeddropwise to a suspension of NaH (1.03 g, 60% in dispersion in oil, 25.75mmol) in DMF. (30 ml) cooled to 0° C. After 30 minutes at 0° C., 2.65 ml(44 mmol) of CS₂ are added, agitation is maintained for 15 minutes andthen 3.51 ml (26.7 mmol) of ethyl-2-bromopropionate are added. Themixture is left at 0° C. for 23 hours, then neutralised by the additionof a saturated solution of NH₄Cl, extracted with ethyl acetate (3 times)and then dried over MgSO₄. After evaporation of the solvents andpurification by flash chromatography (silica, petrol/ethyl acetate 9:1),xanthate IAa is isolated with a yield of 21%.

IR (film) 2982, 2931, 1736, 1450, 1158 cm⁻¹; MS (IC) m/z [MH]⁺; ¹H NMR(MHz, CDCl₃) δ 4.03-4.37 (m, 7H), 1.75 (d, J=6.8 Hz, 3H), 1.20-1.56 (m,9H); ¹³C NMR (50 MHz, CDCl₃) δ 198.0, 170.3, 64.8, 64.7, 61.9, 40.2,28.4, 15.9, 15.8, 13.8.

EXAMPLE 2 Preparation of2-[1-diethoxyphosphoryl)-ethoxythiocarbonylsulphanyl)-propionic acidethyl ester (xanthate IAb)

2.07 ml (16.13 mmol) of diethyl phosphite HP(O)(OEt)₂ are added dropwiseto a suspension of NaH (645 mg, 60% in dispersion in oil) in THF (30 ml)cooled to −78° C. The reaction mixture is agitated at −78° C. for 40minutes, then at 0° C. for 30 minutes. At that temperature, 847 μl(15.16 mmol) of acetaldehyde are then added and the mixture is allowedto return to ambient temperature for 2 hours 30 minutes. 4.8 ml (80.64mmol) of CS₂ are then added and, after 30 minutes at 0° C., 2.08 ml(16.02 mmol) of ethyl 2-bromopropionate are added. Agitation ismaintained for a further 30 minutes and then the reaction mixture isneutralised by the addition of a saturated NH₄Cl solution, extractedwith ethyl acetate (3 times) and then dried over MgSO₄. Afterevaporation of the solvents and purification by flash chromatography(silica, heptane/ethyl acetate 2.8 then pure ethyl acetate), thexanthate IAb is isolated with a yield of 30%.

IR (film) 2983, 2935, 1736, 1641, 1213, 1040 cm⁻¹; MS (IC) m/z 359[MH]⁺; ¹H NMR (200 MHz, CDCl₃) δ 4.11-4.26 (m, 8H), 1.52-1.63 (m, 6H),1.26-1.39 (m, 9H); ¹³C NMR (50 MHz, CDCl₃) δ 198.0, 170.9, 74.6, 74.5,71.9, 71.8, 63.2, 63.1, 63.0, 62.9, 61.8, 47.9, 47.6, 17.1, 16.9, 16.5;16.4, 14.6, 14.1.

EXAMPLE 3 Polymerisation of ethyl acrylate in the presence of xanthateIAa(I)

There are introduced into a Carius tube:

-   -   3.6×10⁻³ mmol of azo-bis-isobutyronitrile (AIBN) (0.6 mg),    -   10 mmol of ethyl acrylate (1 g)    -   0.12 mmol of xanthate IAa (51.5 mg)    -   1.08 cm³ of toluene.

The tube is connected to a vacuum manifold, immersed in liquid nitrogenand then three cycles of “freezing/vacuum/return to ambient” are carriedout on the contents of the tube in order to degas it. It is then sealedunder vacuum. After returning to ambient, it is immersed in an oil bathpreheated to 80° C. The tube is removed from the oil bath after 8 hoursand is immersed in liquid nitrogen in order to stop the polymerisationand to be analysed. The polymer is recovered by opening the tube andthen evaporating the traces of residual monomer.

A check is carried out on:

-   -   conversion into monomer by gravimetry    -   conversion into xanthate (by GPC, UV detection)    -   M_(n) and M_(w)/M_(n) by GPC.

The conversion into monomer is 88.4%.

The conversion into xanthate is 100%.

M_(n) equals 7300 g/mol.

M_(w)/M_(n) equals 1.18.

By way of comparison, a reaction carried out under the same initialconditions of temperature and concentration, the xanthate of the priorart (ethyl a-(O-ethylxanthyl) propionate) (or O-ethylS-(1-methoxycarbonylethyl)dithiocarbonate) leads to a polymer having apolydispersion index close to 1.80.

EXAMPLE 4 Polymerisation of styrene in the presence of xanthate IAa (II)

There are introduced into a Carius tube:

-   -   14.4 mmol of styrene (1.5 g)    -   0.18 mmol of xanthate IAa (74.2 mg)

According to the same experimental protocol as that described in theprevious Example, the reaction is carried out at 110° C. and is stopped,this time after 48 hours, and the polymer is analysed.

The conversion into monomer is 74.4%.

The conversion into xanthate is 100%.

M_(n) equals 6500 g/mol.

M_(w)/M_(n) equals 1.14.

By way of comparison, a reaction carried out under the same initialconditions of temperature and concentration, the xanthate of the priorart (ethyl a-(O-ethylxanthyl)-propionate) (or O-ethylS-(1-methoxycarbonylethyl)dithiocarbonate) leads to a polymer having apolydispersion index close to 2.

EXAMPLE 5 Polymerisation of vinyl acetate in the presence of xanthateIAa (III)

There are introduced into a Carius tube:

-   -   17.4 mmol of vinyl acetate (1.5 g)    -   0.22 mmol of xanthate IAa (89.8 mg)    -   0.013 mmol of AIBN (2.1 mg).

According to the same experimental protocol as that described in theprevious Example, the reaction is carried out at 80° C., then stopped,this time after 8 hours. The polymer is then analysed.

The conversion into monomer is 11.3%.

The conversion into xanthate is 100%.

M_(n) equals 1300 g/mol.

M_(w)/M_(n) equals 1.17.

EXAMPLE 6 Polymerisation of styrene in the presence of xanthate IAa (IV)

There are introduced into a Carius tube:

-   -   43.2 mmol of styrene (4.5 g)    -   0.184 mmol of xanthate IAa (76 mg)

According to the same experimental protocol as that described in Example1, the reaction is carried out at 110° C. and is stopped, this timeafter 48 hours, and the polymer is analysed.

The conversion into monomer is 71.3%.

The conversion into xanthate is 100%.

M_(n) equals 16200 g/mol.

M_(w)/M_(n) equals 1.13.

EXAMPLE 7 Synthesis of a polystyrene-b-ethyl polyacrylate di-blockcopolymer

According to the same experimental protocol as that described in Example1, the reaction is carried out at 80° C., and is stopped, this timeafter 10 hours, and the polymer is analysed.

-   -   3 g of polystyrene IV    -   1.85 g (18.5 mmol) of ethyl acrylate    -   3 mg of AIBN (0.018 mmol)    -   5 ml of toluene

The conversion into monomer is 87.3%.

M_(n) equals 23700 g/mol.

M_(w)/M_(n) equals 1.17.

EXAMPLE 8 Synthesis of a polystyrene-b-t-butyl polyacrylate di-blockcopolymer

According to the same experimental protocol as that described in Example1, the reaction is carried out at 80° C. and is stopped, this time after10 hours, and the polymer is analysed.

-   -   1 g of polystyrene II    -   2.96 g (23 mmol) of t-butyl acrylate    -   2.5 mg of AIBN (0.015 mmol)    -   5 ml of toluene

The conversion into monomer is 91%.

M_(n) equals 21100 g/mol.

M_(w)/M_(n) equals 1.19.

1-10. (Canceled)
 11. Polymer composition that can be obtained by themethod comprising bringing into contact with one another anethylenically unsaturated monomer, a source of free radicals and acompound of formula (IA), (IB) or (IC):

in which: R² and R^(2′), which may be identical or different, representa group of the formula:

in which: R³ and R⁴, which may be identical or different, are selectedfrom the group consisting of a halogen group, —NO₂, —SO₃R, —NCO, CN, R,—OR, —SR, —NR₂, —COOR, O₂CR, —CONR₂, —NCOR₂, and C_(n)F_((2n+1)) with nbeing from 1 to 20, in which the groups R, which may be identical ordifferent, represent H or a group selected from the group consisting of:alkyl, alkenyl, alkynyl, cycloalkenyl, cycloalkynyl, aryl, optionallyfused to an aromatic or non-aromatic heterocycle, alkaryl, aralkyl, andheteroaryl, which are optionally substituted by one or more identical ordifferent groups selected from the group consisting of halogen, ═O, ═S,OH, alkoxy, SH, thioalkoxy, NH₂, mono- or di-alkylamino, CN, COOH,ester, amide, C_(n)F_(2n+1), and/or optionally interrupted by one ormore atoms selected from the group consisting of O, S, N, and P, or aheterocyclic group optionally substituted by one or more groups asdefined above, or R³ and R⁴, together with the carbon atom to which theyare attached, form a group ═O, ═S or a hydrocarbon ring or aheterocycle, R⁵ and R⁶, which may be identical or different, represent agroup as defined above for R, or R⁵ and R⁶ together form a C₂-C₄hydrocarbon chain optionally interrupted by a hetero atom selected fromthe group consisting of O, S and N, R¹ and R^(1′), which may beidentical or different, represent a group as defined above for R³ or R⁴,and p represents an integer from 2 to
 10. 12. Polymer compositionaccording to claim 11, which has a polydispersion index of at most 2.13. Composition comprising predominantly a polymer of the generalformula:

in which: R¹ and R² are as defined in claim 11; V, V′, W and W′, whichmay be identical or different, represent H, an alkyl group or a halogen;X, X¹, Y and Y¹, which may be identical or different, represent H, ahalogen or a group R⁷, OR⁷, O₂COR⁷, NHCOH, OH, NH₂, NHR⁷, NR₂, R₂N⁺O⁻,NHCOR⁷, CO₂H, CO₂R⁷, CN, CONH₂, in which R⁷ is selected from the groupsR as defined in claim 11; a and b, which may be identical or different,are 0 or 1; m and n, which may be identical or different, are higherthan or equal to 1, and when one or the other is higher than 1, therepeating units are identical or different.
 14. Polymer compositionaccording to claim 13, wherein the polymer of the general formula (IIIA)is a homopolymer, the repeating units being identical.
 15. Polymercomposition according to claim 13, wherein the polymer of the generalformula (IIIA) is a block polymer, the repeating units being different.16. Method for the preparation of a composition comprising a multi-blockpolymer according to claim 15, wherein the implementation of the methodis repeated at least once using: monomers differing from those used inthe previous implementation; and instead of the precursor compound offormula (IA), (IB) or (IC), the block polymer resulting from theprevious implementation.
 17. Block polymer according to claim 15, havingat least two block polymers selected from the following associations:polystyrene/poly(methyl acrylate), polystyrene/poly(ethyl acrylate),polystyrene/poly(tert-butyl acrylate), poly(ethyl acrylate)/poly(vinylacetate), poly(butyl acrylate)/poly(vinyl acetate), poly(tert-butylacrylate)/poly(vinyl acetate).
 18. Compounds of the general formulae(IA) to (IC):

in which: R² and R^(2′), which may be identical or different, representa group of the formula:

in which: R³ and R⁴, which may be identical or different, represent ahalogen group, —NO, —SO₃R, —NCO, CN, R, —OR, —SR, —NR₂, —COOR, O₂CR,—CONR₂, —NCOR₂, C_(n)F_((2n+1)) with n being from 1 to 20, in which thegroups R, which may be identical or different, represent H or a groupselected from: alkyl, alkenyl, alkynyl, cycloalkenyl, cycloalkynyl,aryl, optionally fused to an aromatic or non-aromatic heterocycle,alkaryl, aralkyl, heteroaryl, which are optionally substituted by one ormore identical or different groups selected from the group consisting ofhalogen, ═O, ═S, OH, alkoxy, SH, NH₂, mono- or di-alkylamino, CN, COOH,ester, amide, CF₃, and/or optionally interrupted by one or more atomsselected from O, S, N, and P, or a heterocyclic group optionallysubstituted by one or more groups such as defined above, or R³ and R⁴,together with the carbon atom to which they are attached, form a group═O, ═S or a hydrocarbon ring or a heterocycle, R⁵ and R⁶, which may beidentical or different, represent a group such as defined above for R,or R⁵ and R⁶ together form a C₂-C₄ hydrocarbon chain optionallyinterrupted by a hetero atom selected from O, S and N, R¹ and R^(1′),which may be identical or different, represent a group such as definedabove for R³ or R⁴, p represents an integer from 2 to 10, provided that,when R¹ represents an alkyl group, and R³ and R⁴ represent a group R asdefined above, R is necessarily substituted by one or more identical ordifferent groups selected from the group consisting of halogen, ═O, ═S,OH, alkoxy, SH, thioalkoxy, NH₂, mono- or di-alkylamino, CN, COOH,ester, amide, C_(n)F_(2n+1), and/or interrupted by one or more atomsselected from O, S, N, and P.
 19. Compounds according to claim 18,wherein R³ represents an electron-attracting group.
 20. Compoundsaccording to claim 18, wherein R³ represents an alkyl group substitutedby at least one fluorine, chlorine and/or bromine atom, or a cyanogroup.
 21. Compounds according to claim 18, wherein R⁴ represents ahydrogen atom.
 22. Compounds according to claim 18, wherein R³ isselected from the group consisting of: CF₃, CF₂CF₃, and C₆F₁₃. 23.Compounds according to claim 18, wherein R¹ is selected from the groupconsisting of: CH(CH₃)(CO₂Et) CH(CH₃)(C₆H₅) CH(CO₂Et)₂C(CH₃)(CO₂Et)(S—C₆H₅) C(CH₃)₂(C₆H₅), and


24. Compounds according to claim 18, wherein the compound of formula(IA) is selected from the group consisting of:


25. A polymer comprising at least one compound of the general formulaeIA to IC:

in which: R² and R^(2′), which may be identical or different, representa group of the formula:

in which: R³ and R⁴, which may be identical or different, represent ahalogen group, —NO₂, —SO₃R, —NCO, CN, R, —OR, —SR, —NR₂, —COOR, O₂CR,—CONR₂, —NCOR₂, C_(n)F_((2n+1)) with n being from 1 to 20, in which thegroups R, which may be identical or different, represent H or a groupselected from the group consisting of: alkyl, alkenyl, alkynyl,cycloalkenyl, cycloalkynyl, aryl, optionally fused to an aromatic ornon-aromatic heterocycle alkaryl, aralkyl, heteroaryl, which areoptionally substituted by one or more identical or different groupsselected from the group consisting of halogen, ═O, ═S, OH, alkoxy, SH,thioalkoxy, NH₂, mono- or di-alkylamino, CN, COOH, ester, amide,C_(n)F_(2n+1), and/or optionally interrupted by one or more atomsselected from O, S, N, and P, or a heterocyclic group optionallysubstituted by one or more groups such as defined above, or R³ and R⁴,together with the carbon atom to which they are attached, form a group═O, ═S or a hydrocarbon ring or a heterocycle, R⁵ and R⁶, which may beidentical or different, represent a group such as defined above for R,or R⁵ and R⁶ together form a C₂-C₄ hydrocarbon chain optionallyinterrupted by a hetero atom selected from O, S and N, R¹ and R^(1′),which may be identical or different, represent a group such as definedabove for R³ or R⁴, p represents an integer from 2 to 10, for thecontrolled radical polymerisation of ethylenically unsaturated monomers.26. Method for the preparation of compounds of the general formula IAaccording to claim 18, comprising the following steps: a) reacting acarbonyl compound of the general formula II:

R³ and R⁴ being as defined above, with a phosphite of the generalformula III:

R⁵ and R⁶ being as defined above, to form a compound of the generalformula IV:

R³, R⁴, R⁵ and R⁶ being as defined above, b) reacting the compound offormula IV with carbon disulphide CS₂ in the presence of a metalalcoholate M⁺OR′⁻ to yield a xanthate of formula V:R²O(C═S)—S⁻, M⁺  (V) in which R² is as defined above and M+ represents acation. c) reacting the compound of formula V with a compound of formulaVI:R¹X   (VI) in which R¹ is as defined above and X represents a halogenatom, to yield the compound of formula (IA).
 27. Polymer compositionaccording to claim 12, which has a polydispersion index of at most 1.5.